Multiple sclerosis incidence in the era of measles-mumps-rubella mass vaccinations

Viral childhood infections may be involved in the multiple sclerosis (MS) pathogenesis. Following national Swedish vaccination programs, measles sharply declined in the 1970s, and measles, mumps, and rubella were virtually eliminated in cohorts born from 1981. To examine whether the vaccination induced reduction in these infections influences the MS incidence. In addition, the public health aspect justified an early evaluation of beneficial as well as harmful effects of mass vaccinations. From an incidence material of 534 MS patients, born 1959-1990, we selected one unvaccinated cohort and four cohorts, each corresponding to a vaccination program (MS patients = 251). With the ability to detect a decrease by 30-35%, and an increase by 37-48% in the MS incidence in the first three cohorts, we found no vaccination related MS incidence changes. The background MS incidence showed a significant gradual age dependent increase. While the present follow-up provided limited power in the last cohort, there is no evidence as yet that the radical decline in three viral infections influenced the MS incidence. However, the increasing background MS incidence of unknown cause may have concealed a reduction in MS risk associated with mass vaccinations.